Cardiac responses to exercise in the dog before and after destruction of the sinoatrial node.

摘要: Chronotropic and dromotropic responses to treadmill exercise were compared in conscious dogs prior following excision of the sinoatrial node (SAN). The initial junctional rhythm accompanying removal SAN region was replaced within hours days by subsidiary atrial pacemaker (SAP) foci located inferior right atrium along sulcus terminalis. With intact, cardiac acceleration immediate at onset tachycardia directly proportional work intensity. Atrioventricular (AV) conduction concurrently accelerated during as manifest shortening P-R atrioventricular (A-V) intervals. Following excision, likewise demonstrated prompt tachycardias exercise, although heart rate significantly reduced rest steady state exercise. In SAP state, related intensity mediated changes autonomic nerve activity. Combined propranolol-atropine blockade increased attenuated interval resting animal. response AV time decreased though absolute levels not different from control runs with intact. Blood pressure similar both states. We conclude that an unstable period, maintain adequate increases dynamic primarily via regulation.